Field of the Invention
The present invention relates to an image processing technique that optically tracks an object.
Description of the Related Art
A technique that extracts a specific object image from images supplied in time series and tracks the object is utilized for specifying a human face region and a human body region in moving images. The object tracking technique can be used in many fields, for example, teleconferencing, man-machine interfaces, security, monitoring systems for tracking any object, image compression, and the like.
In digital still cameras and digital video cameras, there has been proposed a technique that extracts and tracks an object image in a captured image that is specified by an operation using a touch panel and the like, and consequently optimizes a focus state and an exposure state for the object. Japanese Patent Application Laid-Open Publication No. 2005-318554 discloses an image capturing apparatus that detects (extracts) and tracks the position of a face region included in a captured image, focuses on the face, and captures the image with optimal exposure. Japanese Patent Application Laid-Open Publication No. 2001-60269 discloses a technique that automatically tracks a specific object by using template matching. In the template matching processing, a partial image obtained by cutting out an image region including a specific object image (hereinafter, also referred to as a “tracking target”) is registered as a template image. With the use of an input interface such as a touch panel, any region included in the image is specified, and the template image is registered as serving the region serving as a reference. A specific object can be tracked by calculating an area that is the highest in similarity or an area that is the lowest in dissimilarity in the image by comparison with the template image.
In the template matching processing, the similarity of pixel patterns is used as an evaluation scale. Accordingly, if the pixel patterns in the partial region in the tracking target and the objects other than the tracking target (for example, a background) are similar to each other, an object that should not be tracked may be tracked. As another tracking method, there is a method in which color histogram similarity is utilized as the evaluation scale for matching. In this case, if the proportions of the color in the partial region between the tracking target and the objects other than the tracking target are similar to each other, an object that should not be tracked may be tracked. In order to improve an accuracy of the object tracking, new information for distinguishing the tracking target from the objects other than the tracking target is necessary.